Head Unit Blows Fuses Like Nobodies Business

[Megabunny]

so let me lay down the backstory. its long but please read.

4 Years ago I bought a HUGHES & KETTNER WARP 7 (cab and head)

1 Year ago I began perform to crowds in pubs and larger venues. the WARP 7 was perfect.

6 months ago I began lending it to other performers (I was always there to make sure they weren't abusing my gear)
they'd play for an hour and then the fuse would blow. pop in a new fuse, then an hour or so later .... POP! another fuse.
I'd use it .... for HOURS, 5-6 at a time at 3/4 volume. no problem, fuses all fine. not hot. it was perfect.

last gig it goes after 20 mins. I haven't used it since.

thats the story.

Here is my theory;
-when ever I use my amp I don't use any pedal or stomp box. my setup is Guitar->Head Unit->Speaker Cab.
-everyone used their own effects pedal. usually a fancy multi effects pedal.

I think their pedals output too high a volume (too strong a signal), the amp doesn't like the powerful signal and blows the fuse. my unedited signal is a lower output and it doesn't stress the amp, no fuse damage.


Is this possible? is it bad luck? am I being possessed by demons and blowing my own fuses.

all Ideas are welcome or if you genuinely know what's happening I really want to know.

any comment welcome, I'll answer any questions as best I can, but I'm no Guitar engineer so please keep it simple.

ohh, and the names
Mike.

[Enzo]

Sorry, I don;t think your theory works.


When you loan this out, do those guys use the same cabinet and speaker cord?  Or do they use their own?   How about the power source?

[phatt]

Can you read the labels next to the fuse ,, or next to power cord input?
Reply with what is written there before you worry.
(better still a pic of panel)

Example, 1 Amp @ 240VAC

Cheers, Phil.

[Megabunny]

heres and image of the rear panel
my fuse is 250v 500mah

[joecool85]

The effects pedals wouldn't do it.  Something is wrong with the amp.  Are you electronically inclined?  It would be worth checking for shorts and/or burned out caps in the power supply of the amp.

[Megabunny]

i fix computers for a living so im not uncomfortable with components, im just not sure what im looking for... I'll Google for some burnt diodes and what not, then see if it looks similar inside.

any tell-tale sign to look out for?

[J M Fahey]

Hi Megabunny.
I find 500mA a very small fuse value for your amp, even if it's written so in the back panel.
Is it a 100W SS amp?
It should use a 1A one.
In theory "120VA" power consumption from 220/230V lines would mean slightly over 500mA and fuses usually stand more current than rated, but it's too close for comfort.
Are you using *exactly* the same fuse?
Because it asks for a 500mA *T* type, which means a Time/slow blow/retarded/delay type of fuse.
Maybe you are using regular, not T fuses.
My theory is that there's nothing wrong with your amp, just a *too* tightly specified fuse.
Check that it's a "T" one, and maybe "upgrade" to a 750 mA one.
I usually don't suggest such a thing, but in this particular case the "official" value worries me a little.
Good luck.

[phatt]

If it helps I fixed a Laney Amp in the land downunder (240Vac Aust)
LC 30's kept blowing mains 630mA fuse.
Replaced with 750mA and the unit has not returned well over a year now.

It's actually the reason I asked about the fuse because I've since read that there are apparently some issues with OS gear imported into Australia.

Now do I get a browny point for being so clever?  0:)
Just kidding.

Not sure of the maths but in general the fuse is doubled for 110 ac mains.

But then 110 ac Mains is 60 Hertz and 240 ac Mains is 50 /Hertz.
(headscratch)

Also a point to ponder is the use of donut Xformers they have a bigger inrush at turn on which over time may weaken the fuse element. Again a head scratch,, too deep for my abbacus.
Cheers, Phil.

[Megabunny]

Hi Megabunny.
I find 500mA a very small fuse value for your amp, even if it's written so in the back panel.
Is it a 100W SS amp?
It should use a 1A one.
In theory "120VA" power consumption from 220/230V lines would mean slightly over 500mA and fuses usually stand more current than rated, but it's too close for comfort.
Are you using *exactly* the same fuse?
Because it asks for a 500mA *T* type, which means a Time/slow blow/retarded/delay type of fuse.
Maybe you are using regular, not T fuses.
My theory is that there's nothing wrong with your amp, just a *too* tightly specified fuse.
Check that it's a "T" one, and maybe "upgrade" to a 750 mA one.
I usually don't suggest such a thing, but in this particular case the "official" value worries me a little.
Good luck.

it is a 100watt solid state amp. the fuses iv used have been slow blow or "T" fuses. i'll try a "250v T 750ma" and report back.

thanks guys.


BTW... its spotless inside. caps are all normal size. no bloating or residue. its surprisingly clean considering how dusty my house is. any tips for maintenance? do's and don'ts? although Ive been playing for about 10 years; I never really got into amps. or changing pick-ups. I have my gear unmodded..... STOCK!

on a Different note.
My gig setup ATM is pretty tight:
[AMP-Warp 7 / Guitar-Jackson Kelly (MEGA Glossy Black)] - Heavy Metal Crunch
[AMP-Warp 7 / Guitar-Gibson SG (faded cherry)]             - Clean Jazz Sound
[AMP-Fender Frontman series 100w / Jackson Kelly w/ Floyd Rose + WahWah Pedal] - 80's Metal / Solo Guitar - Looking into a SCHECTER DAMIEN Series 7 String to replace this.

What are you guys setup for?

[Megabunny]

http://www.maplin.co.uk/Module.aspx?ModuleNo=452

These are the ones i will now get
I usually get the 500ma set, but 630ma is the next step up.

I wont be buying till Tuesday so there's plenty of time to reply in case these are.

Iv had a quick scan over my other amps and they all use T500ma fuses.
they range from 75W all the way to a 400W bass head unit.

[J M Fahey]

Hi Megabunny.
I think 630 mA should do the trick, but since you are ordering, pick some 750 mA too.
Worst case, leave them in your spare box.
As for your other equipment, I find reasonable those 500mA ones in the 75W heads, but impossible on the 400W ones, please check again. (unless those are 400W PMPO, about 20W RMS)
Can you please name model of the 400W head, so I google its user manual, or brochure?.
As an example, an Ampeg B2/SVT350 uses a 5A Fuse in 230V and a 10A one in 115V, the 450W SVTPro too, same values.

[Megabunny]

the 400w isn't 500ma, there's a slot for a spare fuse in the holder, I read the spare fuses value. the main holder doesn't even have a fuse. thanks for making me double check that, I haven't ever got it to work and now i know why.

again. when i get those fuses i'll post up the results.

[Megabunny]

Completely forgot to reply to this.
630mah fuse in.
2hour live sesh.
Not a hint of trouble from the amp, it was perfect.


On a more awesome note
Any tips on recording guitar. I've set up a pretty decent studio, but my recording skill is drums and vocals
I'm guessing use my Warp7 and my studio guitar. mic up the amp with a ribbom mic @45 degree angle and use a clean bypass from my guitar as a backup raw recording, to modify and tinker with. Sound good?